This invention relates to franking machines and in particular to the input of data into such machines.
Known franking machines include electronic accounting and control circuits together with non-volatile memory for carrying out accounting operations in respect of accounting data relating to use of the franking machine in franking mail items and maintaining a record of current values of accounting data. The circuits also perform control functions including controlling operation of a printing device to print franking impressions on mail items. It is necessary to prevent unauthorised access to the accounting and control circuits and to the non-volatile memories otherwise tampering with the accounting data could occur which could result in fraudulent use of the franking machine. Accordingly in order to prevent unauthorised access to the accounting and control circuits and to the non-volatile memories and possible tampering with the accounting data, the circuits and memories are housed in a secure housing. Sealed access to the interior of the secure housing is provided for authorised personnel of the postal authority and for authorised service personnel of the franking machine supplier and its agents.
It is known to provide an input/output port in electronic franking machines to enable communication to take place between the circuits of the franking machine and other devices external to the franking machine. Communication may be required between the franking machine and weighscale in order to permit input of weights or postage charges directly from the weighscale to the franking machine circuits or to permit communication with a remote resetting computer to permit remote recrediting of a credit register of the franking machine. However it will be appreciated that the connections of the input/output port of necessity pass through the wall of the secure housing and in consequence pose a risk of breach of the security of the secure housing. Accordingly measures are taken to ensure as far as is practicable that application of unauthorised signals to the connections of the port cannot cause any malfunction of the electronic circuits within the secure housing.
Whereas known franking machines utilise a print drum carrying print dies for printing of the franking impression and when desired for printing a slogan alongside the franking impression, currently proposed franking machines use digital printing techniques for printing the franking impression and slogan. The use of digital printing techniques provides greater flexibility as compared with print dies as to the form of the impression printed. The digital printer is controlled to print a fixed pattern of the franking impression by means of franking print data stored in a memory and this print data is merged with variable postage charge print data and variable date print data output by the accounting circuits so that the printer prints a franking impression comprising both fixed pattern and variable data. Similarly print data defining an advertising slogan may be stored in a memory as described in application entitled FRANKING MACHINE filed in the name of Raymond J. Herbert on the same date as this present application and claiming priority from UK patent application No. 9226811.9. filed 23 Dec. 1992, the disclosure thereof hereby forming part of and being incorporated in this present application.